The problem I see is that mappers cannot control how the cannon ball moves in the map. That is determined by the annimation (with Tequila's model animation for 1.1). The cannon ball would have to be reanimated for each map in order to do attilery. Also, isn't there already a sphere patch mesh in Radiant and in Q3? I am pretty sure you can have a patch mesh in a func_triain or a func_door.